Re: DMP XR-20 - NO DC

[Jim <alarminex@xxxxxxx>]

On Aug 18, 2:52=A0pm, "Bob La Londe" <n...@xxxxxxxx> wrote:
> "Bob La Londe" <onebike...@xxxxxxxxx> wrote in messagenews:j2hl96$tev$1@d=
ont-email.me...
>
>
>
>
>
> > "nick markowitz" <nmarkow...@xxxxxxxxx> wrote in message
> >news:c15f1da0-b149-436b-a324-4a3953926d4a@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> >> On Aug 17, 5:17 pm, Jim <alarmi...@xxxxxxx> wrote:
> >>> On Aug 17, 4:18 pm, "Bob La Londe" <n...@xxxxxxxx> wrote:
>
> >>> > I've got an XR-20 with no DC. Well its about 2.8 volts. Battery lea=
ds
> >>> > and
> >>> > Aux power both. I see no fuse on the board anywhere, so I am guessi=
ng
> >>> > its
> >>> > got circuit breakers. Any suggestions? What gets me is AUX and Batt=
ery
> >>> > are
> >>> > both low/dead. Most panels have separate fuses or circuit breakers =
for
> >>> > the
> >>> > battery and Aux circuits.
>
> >>> I don't know what you've already tried so here's what first comes to
> >>> mind.
>
> >>> Bad rectifier? or the battery leads were reversed? ( I don't know how=
/
> >>> if they have breaker for reversed leads) If the transformer got a
> >>> blast etc............. might have taken out the rectifier. If there's
> >>> no breaker .... settable or self resetting ....... are there any
> >>> permanent fuses on the board or on the back of the board?
>
> >>> If you can find the rectifier, measure the DC output. It's going to b=
e
> >>> unregulated so if you have an analog meter, it'll allow you to better
> >>> guess at the average output. If it is the rectifier you can usually
> >>> replace it pretty easily or substitute four healthy diodes. Alarm
> >>> mfg's pretty much use compressed mud for components. Don't know how
> >>> much you get into circuitry but sometimes the rectifier is good but
> >>> the regulation components are bad. Capacitor or Zener diode ( if they
> >>> still use them anymore). If you can find the regulation components,
> >>> measure on the other side of them to see if you get better DC. If it'=
s
> >>> all good up to that point then ....
>
> >>> If there are breakers and you get a good DC reading after the
> >>> rectifier it could be a bad breaker. You'd have to follow the DC out
> >>> from the rectifier to each of the breakers. Not too easy to do. A
> >>> partial voltage reading could be indication of a bad (not resetting)
> >>> breaker. But since more than one voltage output is bad, it doesn't
> >>> seem like they'd use one breaker for all of them.
>
> >>> Did you check the back of the board for a burned conductor?
>
> >>> If you have another working board, you can use it to get comparison
> >>> voltage readings to determine where it differs.
>
> >>> Or ..... you could just throw it in the garbage and buy another
> >>> board .... :-)
>
> >> Dont forget to power cycle the board some of the newer PTC thermals
> >> have to have power turned off before they reset. =A0have this problem
> >> with vista 32fb etc bell loop when it shorts you have to power panel
> >> all way dawn and back up and it resets
>
> > I do have a good pull on the shelf. =A0I would just replace it with new=
, but
> > I doubt DMP would sell to me anymore. =A0Alternatively I would just swa=
p for
> > a Napco P1632. =A0The system has a couple keypads though so that drives=
 up
> > equipment costs a little.
>
> Ok, I am looking at my good pull right now. =A0No fuses I can find or fus=
ible
> links on the back like FBII either. =A0It doesn't appear to have a single
> components bridge rectifier either. =A0Looks like they installed their ow=
n
> diode ring as there are 4 of them on the board near a modestly large
> capacitor. =A0There is also a small diode in that area. =A0No clue what t=
hat
> would be for except maybe reverse protection. =A0I see a couple component=
s
> that "might" be circuit breakers. =A0Maybe I'll punch the numbers on it i=
nto
> Google later and see what comes up. =A0Lots and lots of transistors, but =
only
> one with a heat sink. =A0Maybe a voltage regulator?-


Scuse me if I'm being to basic, don't know what you know about
regulated power supplies. Here's the most basic regulated power supply
schmatic that I could find with a brief description.

http://www.powersupplycircuitsdiagram.com/

The large component on the heat sink is the regulator. It should be a
flat  three legged semiconductor. If you use the schematic above with
a meter with the power off. put your meter in the resistance mode and
measure the resistance across each of the bridge diodes. In one
direction you should get a direct short. Reverse the meter leads
across the diode and you should get about a .7 Ohm reading. Anything
different means a bad diode. You will likely get an open across one or
more diodes if that's the problem. Take note of which end of the diode
has the band on it so you know which way you're putting the leads on
it. If it's any other component in the circuit it would be easier to
determine what the problem is if you took measurements with the panel
powered up. That's too hard to explain here. You might try to google
"troubleshooting a regulated power supply". It's pretty simple once
you take a look at it for a few minutes.

If it is a diode in the bridge, just about any large diode will do as
a replacement. 50 to 100 volt diodes are pretty cheap at RS and
overkill for this kind of circuit. The big HOWEVER is .....  If you
haven't done any PC board soldering before it's not something that you
want to do without some coaching.